Acceleration Of Charged Particles Research Articles

Relativistic and Ultra‐Relativistic Electron Bursts in Earth's Magnetotail Observed by Low‐Altitude Satellites

AbstractEarth's magnetotail, a night‐side region characterized by stretched magnetic field lines and strong plasma currents, is the primary site for the release of magnetic field energy and its transformation into plasma heating and kinetic energy plus charged particle acceleration during magnetic reconnection. In this study, we demonstrate that the efficiency of this acceleration can be sufficiently high to produce populations of relativistic and ultra‐relativistic electrons, with energies up to several MeV, which exceeds all previous theoretical and simulation estimates. Using data from the low‐altitude ELFIN and CIRBE CubeSats, we show multiple events of relativistic electron bursts within the magnetotail, far poleward of the outer radiation belt. These bursts are characterized by power‐law energy spectra and can be detected during even moderate substorms.

Compound electron acceleration at planetary foreshocks

Shock waves, the interface of supersonic and subsonic plasma flows, are the primary region for charged particle acceleration in multiple space plasma systems, including Earth’s bow shock, which is readily accessible for in-situ measurements. Spacecraft frequently observe relativistic electron populations within this region, characterized by energy levels surpassing those of solar wind electrons by a factor of 10,000 or more. However, mechanisms of such strong acceleration remain elusive. Here we use observations of electrons with energies up to 200 kiloelectron volts and a data-constrained model to reproduce the observed power-law electron spectrum and demonstrate that the acceleration by more than 4 orders of magnitude is a compound process including a complex, multi-step interaction between more commonly known mechanisms and resonant scattering by several distinct plasma wave modes. The proposed model of electron acceleration addresses a decades-long issue of the generation of energetic (and relativistic) electrons at planetary plasma shocks. This work may further guide numerical simulations of even more effective electron acceleration in astrophysical shocks.

Time-dependent Acceleration and Escape of Charged Particles at Traveling Shocks in the Near-Sun Environment

Current multi-spacecraft in situ measurements allow for the investigation of the time evolution of energetic particles at interplanetary shocks (IPs) at small (≲0.1 au) heliocentric distances. The energy spectrum of accelerated particles at IPs was shown by a previous 1D transport model that includes both self-excited plus preexisting turbulence and a term representing the escape of particles from the system to gradually steepen as a result of a finite acceleration-to-escape timescales ratio; such a model was found in excellent agreement with the entire sample of the ground-level enhancement spectra of solar cycle 23. We solve the time-dependent case of such a model in the case of diffusion dominated by preexisting turbulence. The average timescale for particle acceleration at various heliocentric distances, from 1 au down to the inner heliosphere (<0.1 au), is shorter than in the no-escape case, as higher energy particles have a shorter time to accelerate before completely leaving the system into the upstream medium. A simple scaling with time of the time-dependent spectrum is provided. We compare the “nose” structure at a few ∼100s keV protons first measured in situ by Parker Solar Probe in crossing the very fast 2022 September 5 shock at 0.07 au; we find that the nose is reasonably well explained by a lack of the highest energy particles not yet produced by the young shock by both our model and the no-escape version.

Approximate analytical description of the structured laser beam in the far zone.

In the last few years, new ways of structuring light have emerged, with the potential to be used in a wide variety of applications, including materials processing, micro-particle manipulation and charged particle acceleration. One of these techniques is the structured laser beam (SLB). The important advantages of this beam are the simple generation principle using spherical aberration and the potentially infinite propagation range. This makes the SLB a good candidate for use in alignment over long distances or in free space optical communication. However, understanding the distribution of the optical field in such a beam is not trivial and a full analytical description of the SLB is still missing. This paper proposes an approximate analytical scalar description of the SLB complex amplitude, which characterizes the optical field in the far zone with sufficient accuracy for applications such as alignment or optical communication. The proposed approach has been successfully validated through simulations and experimental measurements.

Alfvén waves in the solar corona: resonance velocity, damping length, and charged particles acceleration by kinetic Alfvén waves

Recent advances in heliospheric exploration spurred by NASA’s Parker Solar Probe (PSP) mission require a deeper understanding of the intricate dynamics of the solar corona and wind. This study provides a detailed examination of kinetic Alfvén waves (KAWs) within the 0-10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0 - 10$$\\end{document} RSun range, a region only briefly explored in future PSP passages. Employing the framework of kinetic plasma theory and incorporating a non-thermal Cairns velocity distribution, we investigate the impact of the non-thermal index parameter Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda$$\\end{document} on the resultant resonance velocity vres\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm {v_{res}}$$\\end{document}. The results reveal a notable change in the distance (RSun) over which the particles transport energy and the magnitude of resonance velocity for Λ>0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda >0$$\\end{document}. We also derive the perpendicular resonance velocity vres⊥\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm {v_{res\\perp }}$$\\end{document} and the group velocity vg\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm {v_g}$$\\end{document} expressions of particles and KAWs, respectively. We find that vres⊥\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm {v_{res\\perp }}$$\\end{document} and the normalized group velocity vg/vA\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm {v_g}/\\mathrm {v_A}$$\\end{document} are significantly influenced by Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda$$\\end{document}. In contrast to the resonance speed and group velocity, the damping length LD\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm {L_D}$$\\end{document} of KAWs is evaluated for different parameters. We find that KAWs experience accelerated damping and exhibit an increased damping length for Λ>0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda >0$$\\end{document}. We evaluate KAWs by the influence of the magnetic field, variation in height relative to the solar radius RSun, and the electron-to-ion temperature ratio Te/Ti\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm {T_e}/\\mathrm {T_i}$$\\end{document}. Collectively, these findings illustrate that KAWs not only are important for heating processes but also accelerate charged particles across considerable distances within the solar corona and solar wind regions. The analytical insights gleaned from this study find practical application in understanding wave phenomena in the solar and heliospheric regimes, particularly exploring the role of non-thermal particles in observed heating processes.

ON THE EFFICIENCY OF WAVE-PARTICLE INTERACTION

The efficiency of acceleration of charged particles during cyclotron resonances and acceleration of particles in a vacuum without an external magnetic field are considered. It is shown that the statement formulated in Lawson-Woodward theorem that relativistic particles do not exchange energy with an external electromagnetic wave in a vacuum is not sufficiently justified.

Model of astrophysical jets in magnetic fields of laser relativistic plasmas

A brief review of the results of experimental modeling of cosmic jets in superstrong magnetic fields of laser relativistic plasma is given. It is noted that the development of cyclotron instability with the generation of cyclotron radiation plays a key role in a number of processes in a plasma with a magnetic field — self-localization of plasma in the form of solitons, conversion of rotational motion of plasma into translational motion, cyclotron acceleration of charged particles, separation (stratification) of a plasma jet into separate plasma formations.

Computer modeling of a new type galactic cosmic rays simulator

A new type of a galactic cosmic rays (GCR) simulator, provided at the JINR Laboratory of Radiation Biology, is potentially capable of generating a complex radiation field with inclusions of a variety of ions with a wide energy range and with required abundance at the charged particle accelerators. This complex multicomponent radiation field simulates radiation environment inside a spacecraft during an interplanetary flight, for example, to Mars. The article provides an analytical description of the GCR simulator as well as a description of a specially developed software that enables selection of necessary parameters of a simulator model for creating relevant mixed radiation conditions. The software implements processing of data obtained with Monte Carlo-based FLUKA and PHITS programs, fitting and optimization of model parameters as well as data visualization tools.

Effect of temperature on the wave breaking amplitude of nonlinear relativistic strong plasma waves

AbstractThe wave‐breaking amplitude of a strong nonlinear plasma wave has been determined in a warm plasma. Pseudopotential technique has been adopted to describe the wave‐breaking phenomena in such plasma. The solution is obtained with the consideration that the phase velocity of the plasma wave is equal to the velocity of light in vacuum. This assumption is justified since the wave which is excited usually by the relativistic charged particle bunches or laser pulses has phase speed very close to the speed of light in vacuum. The investigation shows that the breaking amplitude decreases with the increase of the electron temperature. Furthermore, the wavelength of the plasma wave is seen to decrease as we increase the electron temperature. The obtained results have relevance in the astrophysical situation as well as in the field of plasma based charged particle acceleration process.

Experimental apparatus for condensed excited hydrogen research

In this article, we report on a versatile experimental instrument for the study of hydrogen, condensed excited hydrogen, and hydrogen Rydberg matter, charged particles, and radiation from these systems. The system allows researchers to attach different detectors to the chamber to study condensed hydrogen, Rydberg matter, or excited hydrogen under different conditions. We show how the system is used to excite hydrogen to Rydberg atoms while monitoring Rydberg states using lasers and time-of-flight (TOF) on ions with radiation monitoring. We verify some of the work on using clustered hydrogen and laser to accelerate particles from rest to relativistic velocity. The experimental setup is an advanced replication of the reactor and detection system setup reported by researchers from Goteborg University. This experimental instrument can be used to replicate more of the work performed by the research group at Gothenburg University on Rydberg Matter, charged-particle acceleration, and experiments on ultra-dense hydrogen (UDH).

Observation of strong in-plane perpendicular electric field in a radio frequency plasma with a time-varying magnetic nozzle

The spatiotemporal evolution of the electron temperature and plasma potential in a 200-W radio frequency argon discharge with a time-varying (approximately 60 kHz) magnetic nozzle was measured. Unlike in conventional static magnetic nozzles, the two-dimensional profiles of the electron temperature and plasma potential changed in sync with the applied azimuthal electric field, not with the magnetic field. The temporally resolved electric field vectors demonstrated an enhancement of the perpendicular component, where the direction fairly matched that of electron Eθ×B drift, indicating a space charge separation. This observation suggests that the applied time-varying field actively enhanced cross field electron transport, resulting in a unique potential structure and charged particle acceleration.

Angular momentum transfer to charged particles by interaction with Laguerre–Gauss pulses

Orbital angular momentum of light and the associated Laguerre–Gauss modes have garnered increasing interest due to the many applications they promise in the fields of telecommunications and quantum information, as well as charged particle acceleration. Here, we use the numerical simulation of the dynamics of a large number of identical, charged, relativistic, but classical particles, forming a statistical ensemble and seen as test-particles in a time-dependent external electromagnetic field, to get insight into the process of a head-on collision with a pulsed Laguerre–Gauss mode. We have identified two steady-states regimes (low a0 and large a0), where the distribution of the final angular momentum gained by the particles as a function of their initial coordinates is well-behaved and does not change its structure with variations of the reduced amplitude. For small reduced amplitudes a0 of the incoming electromagnetic field, we have also found an analytic approximation of the expression for the angular momentum transferred to the particles after the pulse has left their region. Using both numerical integration and the analytic approximation, we have investigated the effects of the field’s gradient, initial phase of the field, polarization type, and azimuthal order m.

Acceleration of Electrons and Ions by an “Almost” Astrophysical Shock in the Heliosphere

Collisionless shock waves, ubiquitous in the Universe, are crucial for particle acceleration in various astrophysical systems. Currently, the heliosphere is the only natural environment available for their in situ study. In this work, we showcase the collective acceleration of electrons and ions by one of the fastest in situ shocks ever recorded, observed by the pioneering Parker Solar Probe at only 34.5 million km from the Sun. Our analysis of this unprecedented, near-parallel shock shows electron acceleration up to 6 MeV amidst intense multiscale electromagnetic wave emissions. We also present evidence of a variable shock structure capable of injecting and accelerating ions from the solar wind to high energies through a self-consistent process. The exceptional capability of the probe’s instruments to measure electromagnetic fields in a shock traveling at 1% the speed of light has enabled us, for the first time, to confirm that the structure of a strong heliospheric shock aligns with theoretical models of strong shocks observed in astrophysical environments. This alignment offers viable avenues for understanding astrophysical shock processes and the self-consistent acceleration of charged particles.

Joule-class THz pulses from microchannel targets.

Inference of joule-class THz radiation sources from microchannel targets driven with hundreds of joule, picosecond lasers is reported. THz sources of this magnitude are useful for nonlinear pumping of matter and for charged-particle acceleration and manipulation. Microchannel targets demonstrate increased laser-THz conversion efficiency compared to planar foil targets, with laser energy to THz energy conversion up to ∼0.9% in the best cases.

Direct measurements of cosmic – Ray iron and nickel with CALET on the International Space Station

Iron and nickel cosmic ray nuclei play a key role in the understanding of the acceleration and propagation mechanisms of charged particles in our Galaxy. In fact, iron and nickel are the most abundant nuclei among the heavy elements and provide favorable conditions for a low background measurement thanks to the negligible contamination from spallation of higher mass elements. CALET, operating on the ISS since 2015, has excellent capabilities of charge discrimination up to nickel and can measure the energy of cosmic ray nuclei thanks to a lead tungstate calorimeter providing a direct and precise measurement of heavy charged nuclei spectra. In this contribution, a direct measurement of iron and nickel nuclei spectra in the energy range from 10 GeV/n to 2 TeV/n and from 8.8 GeV/n to 240 GeV/n, respectively is presented. More than five years of data collected by CALET were used. A detailed study of systematic uncertainties is also illustrated. The measured spectra are compared with the ones measured by other experiments and are compatible with a single power law fit in the energy region from 50 GeV/n to 2 TeV/n and from 20 GeV/n to 240 GeV/n for iron and nickel respectively. Also, the ratio between nickel and iron spectra is reported.

Triggering the Magnetopause Reconnection by Solar Wind Discontinuities

Magnetic reconnection is one of the most universal processes in space plasma that is responsible for charged particle acceleration and the mixing and heating of plasma populations. In this paper we consider a triggering process of reconnection that is driven by interaction of two discontinuities: solar wind rotational discontinuity and tangential discontinuity at Earth’s magnetospheric boundary, the magnetopause. Combining multispacecraft measurements and global hybrid simulations, we show that solar wind discontinuities may drive the magnetopause reconnection and cause the mixing of the solar wind and magnetosphere plasmas around the magnetopause, well downstream of the solar wind flow. Since large-amplitude discontinuities are frequently observed in the solar wind and predicted for various stellar winds, our results of reconnection driven by the discontinuity–discontinuity interaction may have a broad application beyond the magnetosphere.

A Neutron Beam Shaping Assembly for Boron Neutron Capture Therapy of Superficial Tumors

The Vacuum Insulated Tandem accelerator have been developed in Budker Institute of Nuclear Physics. Neutrons are generated in 7Li(p,n)7Be reaction. Neutron beam shaping assembly is used for therapeutic beam forming. It consists of the moderator, reflector and filter. Magnesium fluoride is considered optimal material for neutron slowing down because of noticeable cross section of inelastic neutron scattering. Previously, we showed that it is optimal to use proton beam at energy 2.3 MeV for neutron generation.As a result of a critical analysis of our earlier decisions on the methods used to form a therapeutic neutron beam and decisions of other research groups, as well as successful experiments on the irradiation of laboratory pets and cell cultures carried out at our experimental facility, we noticed that with the recent trend towards a decrease in proton energy the process of inelastic scattering in MgF2 is no longer decisive in neutron moderation, and it was decided to consider materials based on plexiglass as a moderator material.In this work we considered Poly-Biz as moderator material and get the neutron beam the same quality as with MgF2 moderator and proton energy 2.3 MeV but at lower proton energy and current that can cause treatment time reducing and allows more reliable neutron generation.For a long time, the development of BNСT was hindered by the lack of charged particle accelerators that provide stable production of a stationary 2.5 MeV 10 mA proton beam. The use of BSA with Poly-Biz allows the use of these accelerators at lower energy, which improves the reliability of their operation, and reduces the therapy time by more than 2 times, which is also important for therapy. Also, the use of such an BSA simplifies the requirements for a charged particle accelerator and this opens up both the possibility of optimizing the developed accelerators and the use of other accelerators that have not yet reached the required parameters.

Efficient muon acceleration in laser wakefields driven by single or combined laser pulses

Laser plasma wakefields can provide extremely high fields both in transverse and longitudinal directions, which are very suitable for short-lived charged particle acceleration, such as muons. To get efficient capture and acceleration, we have numerically investigated the acceleration of externally injected muons in laser wakefields driven by usual Gaussian or flying focus lasers. The muons are produced from high-energy electrons interacting with high-Z solid targets, which typically have a broad energy spectrum ranging from hundreds of MeV to several GeV. We classify these muons into three categories according to their initial energies and suggest different drivers for the wakefield acceleration. For low-energy muons (such as E0∼ 600 MeV), as their velocity is much smaller than the phase velocity of a typical wakefield, the optimal driver laser is the combination of a Gaussian laser with a flying focus laser. For moderate-energy muons (such as E0∼ 1.5 GeV), using a Gaussian laser as the driver is the best choice due to its ability to achieve phase-locked acceleration. For high-energy muons (such as E0∼ 5 GeV), in order to avoid dephasing, which usually happens in LWFA, the flying focus laser is suggested to realize phase-locked acceleration. The final muon energies obtained in three cases are 1.2, 2.6, and 6.0 GeV, respectively, with trapping efficiencies of 88%, 92%, and 86%, and the relative energy spread of 2%, 13%, and 10%. Our study demonstrates the possibility for efficient muon acceleration by all optical acceleration with hundred terawatt-class lasers.

New directions in nuclear data research for accelerator-based production of medical radionuclides

Extensive nuclear data studies have been carried out over the last 30 years in the context of accelerator-based production of radionuclides, especially at energies below 30 MeV, and the achieved database is fairly good. Yet there are some deficiencies or new needs of data. Those needs are generally associated with new emerging clinical applications of radionuclides, e.g. theranostic approach, bimodal imaging, radioimmuno-therapy, etc. This article gives an overview of on-going nuclear data research utilizing charged-particle accelerators in four directions, namely low-energy region, intermediate energy range, use of the α-particle beam, and utilization of fast neutrons generated at accelerators. Wherever possible, a comparison of experimental data with theoretical estimates is presented and evaluated (standardised) data, if available, are also briefly discussed.

3D Polarisation of a Structured Laser Beam and Prospects for its Application to Charged Particle Acceleration

A Structured Laser Beam (SLB) is a type of optical beam with spatially inhomogeneous 3D polarisation structures. Generating SLBs from vector beams allows the creation of Hollow Structured Laser Beams (HSLB) with a dark central core. In this way, atypical electric and magnetic field vectors, which are purely longitudinally polarized in the dark zones of the beam, are obtained. The SLB spatial distribution can also include regions with both the electric and magnetic fields longitudinally polarized and oriented in the same or opposite directions. The SLB has a transverse distribution similar to that of a Bessel beam but can theoretically propagate to infinity, therefore giving the potential to generate strong, longitudinally oriented electric fields over long distances, which could possibly allow the acceleration of charged particles. The results of the study of this phenomenon, including simulations of the spatial distribution of the electromagnetic field components, are presented in this paper.